1. Field of the Invention
The field of the invention relates to hypodermic needle assemblies of the type including a pair of telescopically mounted cannulas.
2. Brief Description of the Prior Art
Hypodermic needle assemblies are employed for injecting various fluids within the body, such as medicaments, anesthetics and the like. Such assemblies require cannulas having sharp points in order to penetrate the skin and/or other tissue.
Needle assemblies have been developed which limit the depth of tissue penetration of sharp-pointed cannulas. Collars of enlarged diameter have often been used for this purpose. It is also known to provide a second, blunt-ended cannula telescopically mounted within a sharp-pointed cannula. The second cannula may be advanced beyond the end of the sharp-pointed cannula, and can be used to administer a hypodermic injection at a selected tissue depth. The blunt end thereof reduces the danger of damaging a nerve, a blood vessel of other tissue. U.S. Pat. No. 3,840,008 to Nailes discloses a hypodermic needle assembly of this type.
In the field of ophthalmic surgery, two options are generally available for anesthetization of the extrinsic muscles of the eye. These include retrobulbar and peribulbar injections using conventional, sharp-pointed needles. The retrobulbar technique involves injection of an anesthetic directly into the muscle cone. Akinesia is thereby achieved quickly and thoroughly. However, the introduction of a sharp needle behind the globe must be accomplished very carefully to avoid damaging the optic nerve, perforating the globe, for rupturing blood vessels. Some surgeons have employed dull needles to reduce the possibility of complications, but this makes penetration of the skin more difficult.
Peribulbar injections are administered around the globe rather than behind it. This virtually eliminates the possibility of the above-mentioned complications associated with retrobulbar injections. However, the technique requires a greater volume of anesthetic to be injected, and longer periods of time must be allowed pre-operatively for diffusion of the anesthetic into the muscle cone. Such diffusion must often be aided by external massage or by application of a device known as a Honan Balloon. In addition, the surgeon is not assured to complete akinesia through the use of this technique. Accordingly, there is a need for a device capable of administering retrobulbar injections without the inherent risks associated therewith.